In the scholarly literature devoted to the study of the Nag Hammadi Codices, a system using Roman numerals for each codex followed by an Arabic number in italics for the tractate within that codex is generally accepted. Most scholars add the page and line number of the original Coptic manuscript after the codex and tractate reference, while others omit the tractate reference at times. Thus II,1: 11, 18–22 is a reference to lines 18–22 on page 11 in the first tractate of Nag Hammadi Codex II. This tractate is known as the Apocryphon of John.